#app {
    height: 100%;
    overflow: hidden;
    /* background: black; */
}

img {
    height: 15px;
    width: 15px;
    background: darkcyan;
    transition: 1s height, 1s 1s width;
}

img:hover {
    height: 450px;
    width: 450px;
    animation: 1s rainbow 3;
}

@keyframes rainbow {
    0% {
        background: #c00;
    }
    50% {
        background: orange;
    }
    100% {
        background: yellowgreen;
    }
}

.triangle-topleft {
    width: 0;
    height: 0;
    border-top: 5px solid silver;
    border-right: 4px solid transparent;
    border-left: 4px solid transparent;
}

.container:hover .triangle-topleft {
    border-top-color: #3399ff;
}

.container {
    /* background: darkcyan; */
    width: 14px;
    height: 14px;
    /**/
    border: 1px solid #ccc;
    /**/
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    /**/
    border-radius: 2px;
    box-sizing: content-box;
}

.container:hover {
    border-color: #3399ff;
    background: #dff1ff;
    box-shadow: 0 0 5px rgba(0, 0, 0, 0.1);
}
